Q: What do some of the corrections mean on my typing test?
A: In a short summary, when the punctuations are hi-lighted such as commas, that means they added unnecessary punctuation. If it says something like this: 7×4(-)mm that means what is inside the parentheses is something that should have been there but was not.
I know a lot of this seems very nitpicky and minor but just little changes and omissions can alter the whole meaning of a sentence.